An electrophotographic photoreceptor have been widely applied to an electrophotographic apparatus such as a copying machine, a printer and the like. An inorganic photoconductor having photosensitivity in a visible region, for example amorphous selenium, has been heretofore used as the electrophotographic photoreceptor.
However, the inorganic photoconductor has disadvantage that it contains harmful selenium and cadmium sulfide, and costs for scrapping it become high. Further, the inorganic photoconductor is generally prepared by a vapor deposition method, and costs for producing it become high. The high production cost may also become disadvantage when it is applied to a low-priced machine.
An organic photoconductive substance which is sensitive to semi-conductor laser ray (about 800 nm), has been therefore a matter of interest in the art. A lot of organic photoconductive materials using such an organic photoconductive substance as an active component, have also been proposed. Examples thereof include a negative charging-form organic photoconductor (OPC) which contains a squarylium compound, an azulenium compound, and a phthalocyanine compound as a charge generator. This type of OPC has a conductive substrate, and a photoconductive layer formed thereon. The photoconductive layer comprises a charge generator and a charge transporting material. The OPC is generally classified as those of mono-layered construction and of bi-layered construction.
The conventional OPC, however, does not have sufficient electronic properties such as chargeability, dark decay, and residual potential, and does not have sufficient durability, when it is charged and irradiated repeatedly in the practical use.
Thus, it is desired an organic photoconductive compound which has high sensitivity to visible light or longer-wavelength light, and high durability, when it is used as a charge generator of a charge generating layer (CGL), particularly those of the function separated-form OPC which has bi-layered (CGL and charge transporting layer (CTL)) construction.
Phthalocyanine (This is hereinafter referred to as "Pc".) shows wide variety of electronic properties depending on a kind of the central metal atom bonded thereto, on a kind of the peripheral substituent, and on a kind of preparing process or treating process. It is also known to the art that even if the chemical structure of Pc is equal, when stacking state of the molecules of Pc is different, electronic properties thereof may vary widely.
The stacking state of an organic compound is determined by a polymorph of the compound. That is, the polymorph of the compound determines an electronic state, particularly a perturbation of .pi. electron of the compound. Therefore, the polymorph of the compound is an important factor for improving electronic properties of an organic photoconductive material.
Some Pcs such as titanyl Pc, vanadyl Pc, and X-form metal-free Pc are actually applied to an electrophotographic photoreceptor. Japanese Patent Kokai Publication 98181/1993, 194523/1993, 247361/1993, 11873/1994, and 73303/1994, for example, describe chlorogallium Pc. Japanese Patent Kokai Publication 249716/1993, 263007/1993, and 279591/1993 describe hydroxy gallium Pc having a novel polymorph.
However, photosensitivity and durability of such a conventional OPC are insufficient. There is therefore a need for a novel polymorph of Pc, which may provide an electrophotographic photoreceptor having good photosensitivity and good durability.